A woman walks her dog past a broken block wall in Fullerton, Calif., on March 29 after an earthquake hit Orange County Friday night. / Ken Steinhardt, AP

by Doyle Rice, USA TODAY

by Doyle Rice, USA TODAY

Two strong earthquakes have rattled Southern California in the past 10 days. Is that a sign a bigger one is coming?

It's possible but unlikely, according to CalTech seismologist Kate Hutton, who said there's a "one in 20" chance the two recent quakes would be precursors to a much larger quake.

It does raise the danger for awhile, said University of Washington seismologist John Vidale.

On average, Southern California gets about 10,000 earthquakes each year, according to the U.S. Geological Survey (USGS). That's more than 27 a day.

"Most of them are so small that they are not felt," the USGS says on its website. "Only several hundred are greater than magnitude 3.0, and only about 15-20 are greater than magnitude 4.0."

Southern California gets more earthquakes than any other part of the contiguous USA, Hutton said. She noted that Alaska and the big island of Hawaii see more than California.

A magnitude-5.1 earthquake was felt widely across the region Friday night. The USGS said the epicenter was 1 mile from Brea, about 20 miles southeast of downtown Los Angeles.

"It's the biggest earthquake we've had in Los Angeles in a while," Vidale said, but it's still "a typical Los Angeles earthquake."

Friday's quake hit a week after a predawn magnitude-4.4 quake centered in the San Fernando Valley rattled the region. That jolt shook buildings but did not cause significant damage. Neither quake caused any deaths.

Neither quake was on the famed San Andreas fault, which Hutton said isn't unusual: "A lot of our small quakes are not on the San Andreas fault." Some of the area's bigger quakes, she said, are on the San Andreas.

Southern California has not experienced a disastrous earthquake since the magnitude-6.7 Northridge quake killed dozens of people and caused $25 billion in damage in 1994.